1. Field of the Invention
The present invention is concerned with the manufacture of large surface, quasi-monocrystalline silicon bodies of the type used in solar cells and involves the prevention of carbon penetration from a carbon fabric core into an overlying silicon layer by first providing a silicon carbide surface on the carbon fabric and thereafter applying a substantially pure silicon layer thereover.
2. Description of the Prior Art
In one method of producing large surface, quasi-monocrystalline silicon bodies for solar cells, a reticulate, net-like structure composed of a planar carrier member composed of carbon fibers is brought into contact with molten silicon and the carrier member is integrated into the silicon body by means of crystallization of the silicon. Such a method is disclosed, for example, in DE-OS No. 30 10 557 Al (corresponding to U.S. Ser. No. 238,943, filed Feb. 27, 1981 and now abandoned). This reference discloses a method for manufacturing planar silicon bodies with a high throughput, on the order of one square meter per minute for solar cells. The coating is controlled relative to the drawing rate such that a thin silicon layer is formed in the meshes of the carrier due to the high surface tension of the molten silicon. Consequently, the network consisting of the fibers is integrated in the silicon body after the body has solidified. During the coating, the carrier member is drawn through a gap-shaped opening in the bottom of a melt crucible. The carrier member, however, can also be drawn tanqentially across the surface of the silicon melt in a suitable tank, such as shown, for example, in DE-OS No. 28 50 805.6 (corresponding to U.S. Ser. No. 092,637, filed Nov. 8, 1979, now U.S. Pat. No. 4,305,776).
While a carbon fiber fabric is very well suited as a carrier for silicon because of its temperature resistance and mechanical flexibility, it has the disadvantage that some carbon is dissolved during the coating with silicon. The saturation solubility of carbon in the silicon melt amounts to about 10.sup.18 At/cm.sup.3. As soon as the saturation of the melt with carbon is reached after a brief start-up phase, carbon is introduced into the silicon tape in this concentration. Such an inclusion leads to a reduction in the efficiency of the solar cell fabricated from this material by up to 3%.